1. Field of the Invention
The present invention relates generally to substrate and semiconductor wafer preparation systems and methods, and more particularly, the present invention relates to the drying of substrates and semiconductor wafers following a wet cleaning or processing operation using a combination of an isopropyl alcohol (IPA) assisted Marangoni/Spin relatively low rotational speed drying technique, and a relatively high speed spin drying technique.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform wet cleaning of substrates at various stages of the fabrication process. Wet cleans are designed to wash away any by-products of the fabrication process, remove contaminants, and to achieve and maintain the necessary degree of cleanliness essential to proceed to a subsequent fabrication operation. As transistor device structures become smaller and more complex, the precision required to achieve and maintain structure definition demands exacting standards of cleanliness be maintained in all process operations. If a wet clean is incomplete or ineffective, or if a post-wet clean drying is incomplete or ineffective, then unacceptable residue or contaminants are introduced into the processing environment.
Rinsing and drying techniques, methods, and apparatus are plentiful and known in the art, and incorporate such operations as rinsing and scrubbing, immersion, and the application of thermal, mechanical, chemical, electrical, or sonic energy and the like to remove or displace water and dry the substrate. While some scrub and rinse operations may employ acids or bases for vigorous interaction with fabrication by-products, deionized water (DIW) is commonly used to perform a final rinse before the desired drying technique is performed.
One common drying technique is known as spin, rinse and dry (SRD). SRD uses mechanical, centrifugal, energy to rid the substrate of water by spinning the substrate until dry. FIG. 1A is a block diagram of a typical prior art SRD process. First DIW, or some other rinsing agent, is applied in block 10 to rinse and/or clean the substrate, and then in block 20, the substrate is spun dry.
FIG. 1B shows a typical SRD tool 30. An SRD tool 30 typically includes a chuck 42 within a bowl 48. The chuck 42 is mounted on a spindle 46 that is configured to rotate as shown by arrow 44. A substrate 38 is attached to the chuck 42 with edge holding fingers 40 configured to maintain the substrate 38 in a horizontal orientation, firmly affixed to the chuck 42 so that spinning the chuck 42 on spindle 46 spins the substrate 38 and forces the DIW from the substrate 38 surface. DIW 36, or other processing fluid, is typically dispensed from a dispensing nozzle 34 which is positioned over the substrate 38 at the end of a fluid dispensing arm 32.
In some configurations, the substrate 38 is rinsed while the substrate 38 is spinning to ensure thorough rinsing, and then spun to dry. The spinning of the substrate 38 uses centrifugal energy to force water from the substrate 38 surface, and can be enhanced with the introduction of an inert gas such as Nitrogen or an inert gas vapor to displace any water that is not completely removed by spinning. Additional variations include heating the DIW, heating the SRD environment, heating the inert gas, and the like.
Another common drying technique is known as a Marangoni technique. Marangoni drying (not shown) typically includes using a chemical drying fluid or solvent such as isopropyl alcohol (IPA) to rinse the substrate after rinsing with DIW. The chemical drying fluid or solvent displaces the water on the surface of the substrate, evaporates, and the substrate is dried. Variations of the Marangoni technique also include the introduction of an inert gas such as Nitrogen to enhance evaporation of IPA and exclusion of oxygen, heating the Nitrogen, and the like.
Yet another drying technique that is evolving combines the Marangoni effect with the effects of centrifugal force. Generally, this combination of effects, hereinafter referred to as xe2x80x9cMarangoni/Spin,xe2x80x9d includes the application of DIW or other rinsing agent to a surface of a rotating substrate, and immediately following the application of the DIW with an application of a vapor or gaseous substance so that the vapor or gaseous substance mixes with a trailing edge of the rinsing agent. The trailing edge of the rinsing agent is that region of the film of the rinsing agent near a point of application of the rinsing agent to the surface of the substrate and away from which the liquid film of rinsing agent on the surface of the rotating substrate travels by centrifugal force towards the edge of the substrate.
In Marangoni/Spin drying, the mixing of the vapor or gaseous substance with the liquid rinsing agent on the surface of the rotating substrate produces a mixture that lowers the surface tension of the liquid rinsing agent at the point of mixing. The lowered surface tension forms a defined barrier between the liquid rinsing agent and the vapor or gaseous substance at the trailing edge of the liquid film of the rinsing agent. As the substrate is rotated, the liquid film is forced radially outward from a center region towards the edge of the rotating substrate by centrifugal force. The barrier between the liquid and vapor or gaseous substance confines the liquid portion to the liquid film, and as the film is forced towards the edge of the substrate, the surface of the substrate is left dry with substantially all of the liquid being removed from the surface of the substrate. For further information and discussion of Marangoni/Spin principles and techniques, reference is drawn to U.S. Pat. No. 5,882,433, issued Mar. 16, 1999, and to published European Patent Application EP 0 905 747 A1, published on Mar. 31, 1999, the disclosures of both of which are herein incorporated by reference.
FIG. 1C shows a single-sided substrate drying tool 50 employing Marangoni/Spin drying techniques. The single-sided substrate drying tool 50 includes a chuck 58 mounted on a spindle 62 which is configured to rotate as shown by arrow 60. A substrate 38 is positioned on chuck 58 so that the substrate 38 is spun during the drying process. One or more dispensing arms 52 are positioned over the rotating substrate 38, and are configured to dispense a rinsing agent 56 on the surface of the spinning substrate 38. A vapor or gaseous substance (not shown) is dispensed or introduced immediately following the dispensing of the liquid rinsing agent 56. Nozzle 54 can be configured to dispense both the liquid, rinsing agent 56 and the vapor or gaseous substance, or two dispensing arms 52 can be configured immediately adjacent to one another such that as the dispensing arm 52 or arms are moved from a center region of the spinning substrate 38 towards the edge of the spinning substrate 38, the liquid rinsing agent 56 is dispensed on the surface of the spinning substrate 38 and immediately followed by the vapor or gaseous substance. In this manner, the vapor or gaseous substance mixes with the liquid rinsing agent at the trailing edge of the film of liquid rinsing agent, lowering the surface tension of the liquid film of rinsing agent at the point of mixing, and traveling radially outward on the surface of the spinning substrate 38 as shown by directional arrow 64.
Dual-sided wafer drying has become increasingly desired in substrate processing to meet stringent cleanliness requirements for ever more complex features. A significant limitation in the prior art is generally that methods and apparatus are not disclosed that enable dual-sided substrate drying. FIG. 1C is a typical example showing a single-sided substrate drying tool 50 that positions the substrate on a chuck which effectively blocks access to a backside of the substrate 38. As can be appreciated, even if the illustrated chuck 58 could somehow be modified to provide access to the backside of the substrate 38, there would need to be some mechanism to affix the substrate 38 to the chuck 58 without blocking or significantly limiting access to both top and backside surfaces of the substrate 38, and that would not reflect the liquid film of the rinsing agent back to the surface of the substrate 38.
Whichever method or combination of methods is employed to dry a substrate, effective drying is essential. What is needed is a method of drying a substrate that provides for dual-sided substrate drying, which enables the drying all the way to the edge of the substrate.
Broadly speaking, the present invention fills these needs by providing a method for substrate drying that results in effective substrate drying of both top and bottom surfaces of a substrate. The present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below.
In one embodiment, A method for rinsing and drying a substrate is disclosed. The method includes providing a substrate for processing, and securing the substrate in a hollow spin chuck. The method further includes spinning the hollow spin chuck with the substrate positioned therein at a first rate of rotation. A rinsing agent is dispensed at a position that is an approximate center of the spinning substrate on both an active surface and a backside surface of the substrate, and a surface tension modifying agent is dispensed at the position that is the approximate center of the spinning substrate on both the active surface and the backside surface of the substrate. The dispensing of the rinsing agent and the surface tension modifying agent is then moved from the approximate center of the spinning substrate radially outward towards a periphery of the substrate. The dispensing of the rinsing agent and the surface tension modifying agent is discontinued on both the active surface and the backside surface of the substrate, and the hollow spin chuck with the substrate positioned therein is then rotated at a second rate of rotation.
In another embodiment, a process for cleaning and drying a wafer is disclosed. The process provides for securing the wafer to be cleaned and dried in a hollow spin chuck. The hollow spin chuck provides access to an active surface and a backside surface of the wafer. The process then provides for spinning the hollow spin chuck at a first rate of rotation. A rinsing agent and a surface tension modifying agent are applied to an approximate center of the spinning wafer on both the active surface and the backside surface. The rinsing agent and the surface tension modifying agent are applied immediately adjacent to one another and form a liquid-vapor boundary between the rinsing agent and the surface tension modifying agent. The process next includes moving the applying of the rinsing agent and the surface tension modifying agent from the approximate center of the spinning wafer radially outward towards an edge of the wafer. The moving is configured such that the rinsing agent precedes the surface tension modifying agent radially outward. The applying of the rinsing agent and the surface tension modifying agent is then discontinued, and spinning of the wafer is set to a second rate of rotation.
In still a further embodiment, a Marangoni/Spin method of simultaneously rinsing and drying an active surface and a backside surface of a substrate is disclosed. The Spin/Spin method includes securing the substrate in a hollow spin chuck, and then spinning the hollow spin chuck and the wafer secured therein at a first rate of rotation. A rinsing agent is dispensed to the active and backside surfaces of the spinning substrate at an approximate center of the substrate, and a surface tension modifying agent is likewise dispensed to the active and backside surfaces of the spinning substrate at the approximate center of the substrate. The dispensing of the rinsing agent and the surface tension modifying agent to the active and backside surfaces of the spinning substrate is then moved from the approximate center of the substrate radially outward towards a periphery of the substrate. The moving is configured such that the rinsing agent precedes the surface tension modifying agent moving from the approximate center towards the periphery of the substrate. The first rate of rotation is gradually decreased as the dispensing of the rinsing agent and the surface tension modifying agent is moved. The dispensing of the rinsing agent and the surface tension modifying agent is discontinued, and the spinning of the hollow spin chuck and the wafer secured therein is increased to a second rate of rotation.
The advantages of the present invention are numerous. One notable benefit and advantage of the invention is both the top surface and the backside surface of a substrate are simultaneously dried.
Another benefit is that the present invention is configurable for a plurality of substrate types and sizes. Any of a plurality of substrates requiring wet cleaning or wet fabrication processing, followed by a drying operation can be implemented in an embodiment of the present invention. The rate of rotation can be optimized for a particular size and type of substrate, and the specific rinsing and surface tension modifying agents can be modified for specific applications.